Heretofore difficulty has been experienced manufacturing accurate tooling for testing the mask-wafer stage motion and the mask-wafer stage alignment in optical lithographic projection systems. Suitable projection systems of this type include, for example, Micralign machines, as manufactured by The Perkin-Elmer Corporation, Norwalk, CT.
In the past, test masks were made in the laboratory by scribing thereon a pair of crosshairs, one on one side and the other on the opposite side. Test wafers were also made in the lab, usually from aluminum, by scribing a pattern thereon. Then a lithographic projection system was tested by using a microscope to view between the mask and the wafer, e.g., the line of the mask cutting across the wafer pattern was observed. This was merely a pass or no pass test. The degree of resolution was not determined.
The present contribution to the art is a new system, which is an improvement over such prior art systems, as will become apparent as the description proceeds.